Biomedical Engineering Reference
In-Depth Information
variations in the number of gas moles taken into account. Based on the obtained
с
Н
о
values,
the standard enthalpy of HTS formation (
f
Н
о
) in a solid state at 25
о
С was calculated using
f
Н
о
(Н
2
О, l)= 285.830 0.042 J/mol and
f
Н
о
(СО
2
, g)= 393.51 0.13 J/mol [13].
Figure 3. Thermograms of PMA (4) and its mixture with chitosan (3) obtained at three repeated heating
cycles: (1) the first, (2) the second, (3) the third. The PMA vitrification temperature in mixtures with
chitosan as a function of water concentration in them (B).
3.
R
ESULTS AND THEIR
D
ISCUSSION
The obtained experimental results are presented in Figure 1-5, while the averaged
transition temperatures are listed in Table 1. The performed investigations showed that initial
air-dry specimens contained 4.4-8.9 mass% of adsorption water which evaporated from them
at 120-132
о
С (Figures 1-5, curves 1, Table 1).
Several relaxation transitions (a -transition and two devitrification ones) were observed
in dehydrated CHS (Figure 1, curves 2 and 3). It is attributed to a complex molecular and
supramolecular structure of the given polysaccharide. The -transition in CHS is related to
oscillations of pyranose rings around a glucoside bond. Chitin and other polysaccharides
studied by us behave themselves in a similar manner [10, 14-24]. Irrespective of the source of
initial chitin, a distinctive feature of chitosan [21] is two-stage destruction accompanied with
the release of energy in the form of heat (t
dest1
= 302
о
С, t
dest2
= 328
о
С) (Figure 1, curve 3). The
loss of mass in this case is 41% (Table 1).
The results of the experiments of determining of the energy of CHS combustion are given
in Table 2. The calculated values of Δ
c
U
о
,
c
H
о
and
f
H
о
in the solid state at 298.15 K are
kJ/mol: −3154.9±13.4 kJ/mol, 3155.6±13.3 kJ/mol and 777.55±13.3 kJ/mol, respectively.
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